The global demand for energy continues to rise while reserves of conventional petroleum (e.g. oil, gas, and natural gas liquids) are in decline. This has led to increased focus and research into unconventional fuel resources (e.g. heavy oil, oil sands, oil shale) and other non-fossil sources of energy (e.g. lignocellulosic materials).
A significant amount of research in the field of “alternative” energy production has focussed on the generation of biofuels from lignocellulosic matter. This technology raises the prospect of a shift to an abundant and renewable feedstock for energy production as an alternative to the depleting reserves of hydrocarbon-based raw materials. The enrichment of low energy density fossil fuels (e.g. lignite, peat and oil shale) into high energy fuel products also represents an attractive alternative given the relative abundance of those resources.
In particular, the thermochemical conversion of biomass and other complex organic matter into biofuels and chemicals based on hydrothermal reactions has shown significant promise. Gasification processes are generally conducted at higher temperatures (e.g. 400° C.-700° C.) and can produce methane or hydrogen gases in high yields. Liquefaction processes are generally conducted at lower temperatures (e.g. 200° C.-400° C.) and produce liquid products referred to in the field as “bio-oil” or “bio-crude”. To provide a viable replacement or supplement to existing fossil fuels, bio-oils generated from these and related technologies need characteristics (e.g. high energy/yield, low oxygen/water content, reduced viscosity) approximating those of crude oils. Additionally, it is highly important for processes of this nature to be cost-efficient for economic feasibility.
Numerous modifications to improve thermochemical processes for bio-oil production have been developed. For example, the prior removal of hemicellulose under mild conditions from plant materials can improve the production of bio-oils from lignocellulosic feedstocks (see PCT publication No. WO 2010/037178). It has also been demonstrated that rather than gradually heating feedstock slurry to reaction temperature, contacting the slurry with an already supercritical solvent can provide advantageous effects in bio-oil production (see PCT publication No. WO 2012/000033). Incorporating oil into a feedstock slurry, which may also be a recycled bio-oil product, has been shown to improve process efficiency and product characteristics (see PCT publication No. WO 2012/092644). The inclusion of a solid substrate in organic matter feedstock used in thermochemical conversion processes has been shown to reduce scaling and/or reduce the development of pressure differentials during treatment (see PCT application No. PCT/AU2014/00601). Despite these advances, new modifications to thermochemical processes capable of increasing process efficiency, lowering costs and/or improving product characteristics are still desirable.
Many if not most processes for the thermochemical conversion of biomass into biofuels utilise catalysts to increase process efficiency and/or improve product characteristics. A wide range of catalysts have been used in these processes (see, for example, PCT publication No.
WO 2011/123897) and the identification of appropriate catalyst combinations and/or alternative sources of catalysts provides an opportunity to improve existing bio-oil production methods.